Manufacture of Cable Bolts

ABSTRACT

A cable bolt comprising a plurality of flexible steel filaments formed around a central member, the cable bolt having spaced bulbous portions along the length of the bolt each bulbous portion defining a cavity containing a segmented ring that surrounds the central member to engage the filaments of the bulbous portion.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application is a divisional of U.S. patent application Ser. No.13/852,503, filed on Mar. 28, 2013, which claims priority to AU2012901303, filed on Apr. 2, 2012, the disclosures of which areincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to cable for use in strata control, especially toreinforce the roof and/or walls of underground mines and tunnels, tomethods of manufacturing cable bolts and to manufacturing components andsystems used in such methods.

2. Description of Related Art

Cable bolts are usually made from cable comprising a plurality of steelfilaments wound together around a central wire to form a tendon. Resinand/or cement grout is used to fix the cable bolt to a borehole. Toincrease the effective bond strength between the cable bolt and resin orgrout the bolts are often provided with spaced protuberances along thelength of the cable. These protuberances are often known as bulbs orcages. The protuberances assist in preventing cable bolts from beingpulled through the resin or grout, thus providing improved anchorage andload transfer between the cable, resin/grout and the surrounding strata.

It is known that tensioning of the cable prior to cement grouting cancause the protuberance to collapse thus reducing the cable'seffectiveness. In Australian patent 2004260817 there is a proposal toinsert ball bearings into the cavities defined by the protuberances toreduce the likelihood of the protuberances collapsing when the cable istensioned. This proposal has proved expensive to manufacture andunreliable due to the ball bearings being pushed out of theprotuberances. There is also a need to displace the central wire tolocate each ball bearing. In some cable bolts the central wire isreplaced by a hollow tube which extends along the centre of the cable.Other disadvantages relate to the difficulty in automating the placementof the ball bearings and the ball bearing creates a stress concentrationon the strands of the cable creating loads that lead to failure loads upto 25% less than the original strands ultimate tensile strength.

In our earlier Australian patent application 2008200918 we disclose acable bolt having a hollow strand which facilitates the passage of groutalong the cable. It is important that the hollow strand does not getcrushed by radial loads in non collapsible protrusions.

It is these issues that have brought about the present invention.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided acable bolt comprising a plurality of flexible steel filaments formedaround a central member, the cable bolt having spaced bulbous portionsalong the length of the bolt each bulbous portion defining a cavitycontaining a segmented ring that surrounds the central member to engagethe filaments of the bulbous portion.

In accordance with a further aspect of the present invention there isprovided a method of manufacturing a cable having twisted flexible steelfilaments over a central member, the method comprising forcing thefilaments apart without plastically deforming the filaments, inserting aspacer through the parted filaments to sit between the filaments and thecentral member, and releasing the parted filaments to return against thespacer to form a bulbous portion.

In one form, the filaments are forced apart by applying torsion to thefilaments. In one form, the torsion is applied over a length of thecable to form bulbous portions spaced along the cable.

In one form, in addition to or instead of, the filaments are forcedapart by inserting a spreading tool between the filaments.

In one form, the spacer extends around the central member. In aparticular form, the spacer is a segmented ring that is placed in piecesthrough the parted filaments and formed into a ring surrounding thecentral member. In another form, the spacer may be a unitary element,such as helical wound member that is rotated onto the inner memberthrough the parted filaments.

In one form the torsion and/or spreading is applied over a section ofthe pre-wound cable to open the outer filaments over a set length toallow insertion of the ring segments around the central member beforereleasing the filaments forming a permanent non-collapsible singleprotrusion. The process may be repeated further along the pre-woundcable.

In a further aspect of the present invention, there is provided anapparatus for forming bulbs in a cable having twisted flexible steelfilaments over a central member, the apparatus comprising:

a bulbing assembly releasably engagable with said cable, said assemblybeing operative to force the filaments apart without plasticallydeforming the filaments; and

an inserting device operative to insert a spacer through the partedfilaments to sit between the filaments and the central member.

In use on releasing the parted filaments they return against the spacerto form a bulbous portion in the cable.

In one form, the apparatus further comprises a frame; and a securingdevice for holding at least a portion of a cable with respect to frame.

In one form the cable is fed through the bulbing assembly so that aplurality of bulbing portions are able to be formed along the cable.

In another form, the bulbing assembly is movable relative to theapparatus frame to form spaced apart bulbing portions in the cable.Typically in this latter arrangement the cable remains stationary duringforming of the plurality of bulbs but in another form, the cable may bemoved so that both the cable and the bulbing apparatus move during bulbforming.

In one form, the apparatus includes a feed assembly to feed the cablefrom a coil into the apparatus. In one form the cable, with bulbs formedtherein, is progressed to a table and the apparatus further includes acutting device to cut the cable to length as required in formation ofcable bolts.

BRIEF DESCRIPTION OF DRAWINGS

An embodiment of the present invention will now be described by way ofexample only with reference to the accompanying drawings in which:

FIG. 1 is a part sectioned side view of a typical cable bolt,

FIG. 2 is a cross sectional view of the cable bolt,

FIG. 3 is a schematic view of an apparatus for forming bulbs in a cablein accordance with an embodiment of this invention,

FIG. 4 is a plan view of a bulbing apparatus of the apparatus of FIG. 3,

FIG. 5 is a detailed view of the bulbing apparatus of FIG. 4,

FIG. 6 is a perspective view of the bulb illustrating insertion of asegmented ring. For convenience components of the bulbing apparatus arenot shown; and

FIG. 7 is a perspective view illustrating the location of the segmentedring on a central strand of the cable bolt.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 illustrate a cable bolt 10. These drawings are taken fromour earlier Australian patent application 2008200918, corresponding toU. S. Pat. No. 8,322,950, incorporated herein by reference.

As illustrated in FIG. 1, an embodiment of a resin anchorable cable bolt10 comprises a flexible cable 11 formed from a plurality of woundco-extending strands in the form of wound co-extending steel filamentsthat extends along an axis C between opposite ends (being, relative tothe direction the bolt 10 is installed in a bore in a substrate, such asa mine shaft roof, a distal end 13 and a proximal end 14). The cable 11has a first portion 15 adapted primarily for resin point anchoring, anda second portion 16 adapted predominantly for cement grouting.

As illustrated in FIG. 2, the filaments comprise nine outer steelfilaments 12 a spiral wound about a central hollow filament, or strand12 b, located axially within the cable 11. In one form, the hollowstrand 12 b may comprise at least one region for resisting radialcompression, in particular of a tensioning assembly which is discussedin more detail below. In alternative arrangements, the hollow strand 12b may be plain, and/or more or fewer outer steel filaments 12 a may beused, in which case their relative diameter with respect to the hollowstrand 12 b would be adjusted accordingly such that they are closefitting about the hollow strand 12 b. The outer steel filaments, orstrands, 12 a are typically solid and of the type used for cable bolt orpre-stressed concrete applications. The hollow strand 12 b extends inthe second portion 16 and not in the first portion 15, however inalternative embodiments, the hollow strand may extend into the firstportion 15 also.

In the embodiment of FIG. 1, the central hollow strand 12 b comprisesprofiling allowing flexibility of the cable 11, while providing strengthto resist crushing of the strand (i.e. radial compression of the cable).The hollow strand 12 b is flexible to allow coiling of the cable 11 suchthat the coil has a minimum diameter of 1.2 m without kinking the hollowstrand 12 b. In alternative embodiments, the minimum coiling diameterwithout kinking the hollow strand may fall within the range of 0.8 m to2.5 m, or 1 m to 2 m. In the embodiment illustrated in FIG. 1, theprofiling is in the form of a helical or spiral ribs 17 (see FIG. 7)along its entire length. The hollow strand 12 b is formed from a metalmaterial, in this embodiment steel, but may be formed from a polymericmaterial, such as polypropylene, a polyethylene, or other appropriatepolymer.

Referring again to FIG. 1, the cable bolt 10 further comprises a resinretainer 22 disposed between the first and second portions 15, 16 of thecable 11. The resin retainer 22 is affixed to the cable 11 and extendsradially outwardly from the cable so as to substantially reduce themigration of resin from the first portion to the second portion withinthe bore during point anchoring of the bolt 10. The resin retainer istypically formed from metal, however may be formed from any suitablepolymer such as polypropylene or a polyethylene.

The hollow strand 12 b is located in the second portion 16 of the cablebolt 10 and extends from the proximal end 14 of the cable 11 to alocation 24 in the second portion 16 at or adjacent the retainer 22. Asillustrated in FIG. 1, a nut 26 is located on or near the hollow strand12 b at location 24 within the outer filaments 12 a, forming a bulb, or“nut cage” 28. The nut cage is formed by spacing apart and forcingoutwardly all of the steel filaments 12 along a discrete section of thecable 11 and placing the nut 26 about the hollow strand end 24.

The first portion 15 includes an end collar 31 for holding together thestrands 12 a at the distal end 13, and a plurality (three in theillustrated case) of radially outwardly extending resin mixingprotrusions in the form of “bird cages” 32, where a ball bearing (orother rigid object) is inserted in a partially unwound portion ofstrands 12 a.

It is desirable in some instances to form bulbs along the second portion16 (in addition to the first portion 15) and/or to extend the hollowstrand 12 b into the first portion 16. As such it is desirable to beable to form bulbs about the hollow strand 12 b. Further to facilitatemanufacturing processes, it is desirable that the bulbs are formedwithout unwinding of the steel filaments.

FIGS. 3 to 6 illustrate an apparatus for forming non collapsible spacedprotrusions (or bulbs) 18 about the hollow strand 12 b of the flexiblecable 11. These bulbs 18 incorporate a segmented ring 40 (FIG. 7) thatprevents collapse of the bulb 18 whilst ensuring against radialcompression of the hollow strand 12 b.

The method of forming the bulbs 18 and locating the segmenting ring 20is discussed with particular reference to the bulbing apparatus 100shown FIGS. 3 to 5.

As best shown in FIG. 3, the apparatus 100 includes a bulbing assembly102 mounted on a frame 104. A cable 11 is arranged to be fed from a coil(not shown) mounted within a coil handler 106. Once bulbs are formed inthe cable 11 (as discussed in more detail below) by the bulbing assembly102, the cable is progressed to a payout table 108. A cutting device 110is disposed between the frame 104 and the payout table 108 and isarranged to cut the cable once a desired length (typically of 8 m but itmay be more or less depending on requirements) is passed onto to thetable. The cut lengths of cable can then be further processed to formthe final cable bolts as required. The bulbing process is preferablyfully automated and controlled by a control system 112 which mayinclude, as illustrated, a control cabinet 114 and operator interface116.

As best shown in FIGS. 4 and 5, bulbing assembly 102 includes threecomponents; namely torsioning device 118, spreader 120, and inserter122. In general, the torsioning device 118 is designed to twist thecable bolt 10 to force the filaments 12 a apart to define a gap. Thespreader 120 (shown in the form as a pair of plates or knives 56,57) isdesigned to further spread adjacent filaments that allows the inserter122 adequate space to enable the segmented ring 40 to pass through theparted filaments 12 a to be located in an interfitting arrangement onthe central strand 12 b.

In the illustrated embodiment, the torsioning device 118 discloses theuse of mandrels 51, 52 positioned around the cable 11 at spacedintervals to define a length of cable as shown in FIGS. 4 and 5. Eachmandrel 51 or 52 includes a three jaw chuck 53, 54 which can be broughtinto clamped engagement with the periphery of the cable 11. The chucks53, 54 are clamped to the cable and are either rotated in oppositedirections or one is rotated relative to the other to place thefilaments 12 a of the cable into torsion which has the effect of partingthe filaments 12 a and forming a protrusion 18 at the mid span of cablebetween the chucks 53, 54. With the chucks 53, 54 held in position tomaintain the torsion, spreader knives 56, 57 are pushed between selectedparted filaments 12 a and rotated to further move the filaments apart.This provides access to the inserter 122 (in the form of robotic arms59, 60) which place segments 41, 42 of the ring 40 on opposite sides ofthe hollow strand 12 b and then fitted together as shown in FIGS. 6 and7.

As shown in FIG.7, each ring segment 41, 42 has a projection 43 that isa snug fit within a similarly profiled recess 44 on the other segment 42of the ring to allow the segments 41, 42 to form a circular one piecering 40 as shown in the left hand side of FIG. 6. Once the ring 40 hasbeen placed on the central strand 12 b the knives 56, 57 can be removedand, the torsion applied by the mandrels 51, 52 can be released causingthe parted filaments 12 a to close onto the periphery of the ring 40thereby locating the ring 40 in the cavity of each protrusion 18 on thecentral strand 12 b. By a steady release of the torsional load theparted gap between the filaments closes and the filaments 12 a contactthe ring 40 to form an expanded non-collapsible bulb 18.

The location of the ring 40 on the hollow central strand 12 b ensuresthat when the cable bolt is tensioned the protrusion 18 does notcollapse. The segmented ring 40, by forming a single annular ringensures that there is no danger of the segments 41, 42 crushing thecentral strand 12 b. The dovetailed inter fitting of the segments 41, 42ensure that radial forces on the ring 40 are evenly distributed aroundthe periphery of the strand 12 b. The segmented ring 40 whilstpreventing radial collapse of the strand 12 b can also allow a degree ofmovement between the strand 12 b and ring 40 thus maintaining theflexibility of the final cable.

In the form illustrated, the torsional and spreading forces that areplaced on the cable bolt as it is twisted through use of the mandrels51, 52 and spreader 120 is insufficient to cause plastic deformation ofthe wire filaments 12 a.

Once the bulb 18 is formed, the cable 11 can then be fed through thebulbing assembly 102 (in a direction towards the payout table 108) sucha subsequent portion of the cable 11 aligns with the bulbing assembly.The bulbing assembly is then able to form a further bulb 18 in the cableallowing separate spaced bulbs 18 to be formed in the cable 11.

In an alternative form, the bulbing assembly may be designed to movealong the length of the cable 11 to form spaced apart bulbs in the cable11. In either process, in this manner the cable 11 can have noncollapsible grouting protrusions (in the form of bulbs 18) at desiredintervals along the length of the cable 11.

This process can be completed off a reel and wound back into smallerreels; or to cut to lengths. Alternatively, the process can use precutlengths.

It is also envisaged that the mandrels 51, 52 and chucks 53, 54 may besplit to facilitate attachment to the cable 10 without the need to passthe cable through the mandrels and chucks.

It is to be understood that, if any prior art publication is referred toherein, such reference does not constitute an admission that thepublication forms a part of the common general knowledge in the art, inAustralia or any other country.

In the claims which follow and in the preceding description of theinvention, except where the context requires otherwise due to expresslanguage or necessary implication, the word “comprise” or variationssuch as “comprises” or “comprising” is used in an inclusive sense, i.e.to specify the presence of the stated features but not to preclude thepresence or addition of further features in various embodiments of theinvention.

1. A cable bolt comprising a plurality of flexible steel filamentsformed around a central member, the cable bolt having spaced bulbousportions along the length of the bolt each bulbous portion defining acavity containing a segmented ring that surrounds the central member toengage the filaments of the bulbous portion.
 2. A cable bolt accordingto claim 1, wherein segments of the segmented ring include interfittingprojections and recesses that interengage on assembly of the ring.
 3. Anapparatus for forming bulbs in a cable having twisted flexible steelfilaments over a central member, the apparatus comprising: a bulbingassembly releasably engagable with said cable, said assembly beingoperative to force the filaments apart without plastically deforming thefilaments; and an inserting device operative to insert a spacer throughthe parted filaments to sit between the filaments and the centralmember.
 4. The apparatus according claim 3 wherein on releasing theparted filaments they return against the spacer to form a bulbousportion in the cable bolt.
 5. The apparatus according to claim 3 furthercomprising a securing device for holding at least a portion of a cable.6. The apparatus according to claim 3, further comprising a frame andwherein the bulbing assembly is movable relative to the frame so that aplurality of bulbing portions are able to be formed along the cable. 7.The apparatus according to claim 3, wherein the cable is fed through thebulbing assembly so that a plurality of bulbing portions are able to beformed along the cable.
 8. The apparatus according to claim 3, furthercomprising a cable feeding device operative to feed the cable into thebulbing assembly.
 9. The apparatus according to claim 3, furthercomprising a cutting device to cut cable, the cutting device beingarranged to cut the cable incorporating one or more bulbing portionsinto discrete lengths.